This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Separase is an enzyme that triggers chromosome segregation through the cleavage of cohesin, the protein complex that holds chromosomes together. We recently identified the protein phosphatase 2A, coupled to its regulator, Cdc55, as an important inhibitor of separase (Clift et al., 2009). Separase and Cdc55 are known to form a complex (Queralt et al., 2008), leading to the model that PP2A-Cdc55 inhibits separase by direct dephosphorylation. The aim of this project is to test this model.